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Nov 18, 2007, 02:47 PM
Planes are cool ;)
Hughbert's Avatar
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Build Log

SnakeBipe (previously Simple Indoor Bipe)


Oh no, not another profile bipe! Its been done before, but I’m throwing in my contribution anyway. Pretty much every aspect of this plane was inspired by something I’ve seen here on RCgroups, so to everyone a big thank you!

After finishing a mini-infineon, which is an awesome plane but a little nippy for my indoor *ahem* skills, and since I had a load of EPP just waiting around, I thought I’d try my hand at designing. I’ve done a couple of self-builds before, but nothing spectacular.

This is the first time I put a load of ‘work’ into a design, i.e. calculating things. Hopefully my maths will turn out ok. I also tried really hard to build this one to a target weight, which I achieved - something I’ve never done before!

Plans are a little bit messy and need cleaning up - because my laptops down at the moment and I have no CAD facility, I had to draw plans by hand at half scale, scan them on to the computer and resize them. However this turned out to be a lot of fun (I like drawing) so I’ll probably do it again, even after my laptops fixed.

Setup -
EMax 2805 1600 Kv brushless with 8 x 6 GWS prop
6 amp oem-rc brushless ESC
2 x 3.8g servos
1 x 4.6 g servo (ailerons)
GWS Naro 4ch receiver

Either 2 cell 460mAh (30g) or 2 cell 800mAh (50g), but I’ve got some 500mAh (around 30g) in the post

All EPP is 5mm. About 2 metres of 2mm CF and 1 metre of 3mm CF were used.

Total weight without battery is around 125g, so AUW is around 160-180g. This gives an uppermost wing loading of about 11 g/dm^2, which should suffice.

Edit

After an indoor session (see post 16) the motor mount was cracked again and I decided to change the fuselage (see post 18). I've now added a picture of Version 2.

Edit 2

plans are up!
Last edited by Hughbert; Dec 06, 2007 at 10:56 AM.
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Nov 18, 2007, 02:50 PM
Planes are cool ;)
Hughbert's Avatar
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Steps 1 and 2


Step 1 - Cut out foam from plans. Note - plans need cleaning up before properly usable (check interest). Bevel all hinge surfaces.

Step 2 - Glue one horizontal fuse side to vertical fuse, with 2mm CF rod running on upper side (I actually added the CF rods later to increase stiffness). Choose servo placement and cut out servo holes. Glue servos in place.

I decided to place the aileron servo high in the fuse, and connect to the upper wing ailerons to create more space on the lower fuse for electronics.
Nov 18, 2007, 02:51 PM
Planes are cool ;)
Hughbert's Avatar
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Steps 3 and 4


Step 3 - Add other horizontal fuse side and CF rod. When dry, add 2mm CF rod to stiffen horizontal stabilizer.

Step 4 - Attach rudder/elevator. Connect to servos (I did this after attaching the wings - no real difference)

Apologies for the poor picture quality, they're mostly on my phone camera
Nov 18, 2007, 02:54 PM
Planes are cool ;)
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Step 5


Step 5 - Glue 3mm CF rod to both wing LEs, and 2mm CF to the wing struts. Bend EPP to give the aerofoil shape and attach ailerons. Glue fuse, bracing and wing struts to lower wing, making sure all are square. Attach top wing.

This structure proved pleasingly strong and rigid
Nov 18, 2007, 02:56 PM
Planes are cool ;)
Hughbert's Avatar
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Step 6 and finishing


Step 6 - Attach motor to firewall and firewall to fuse. Connect electronics and adjust trimming.

Voila!
Nov 18, 2007, 03:01 PM
Planes are cool ;)
Hughbert's Avatar
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Maiden report


Maiden 1;
This Saturday had very still weather, although cold and foggy, so on that misty midlands morning me and my dad headed out to our local flying site.

Decided to try my new creation first; revved up and let her go. The EMax motor on the 8x6 had stacks of power, the plane pulled straight into a vertical climb. Input a lot of down elevator to level off and it became obvious that in present condition the plane was near enough uncontrollable And VERY manoeuvrable (read unstable!)

Assuming that the difficulty was due to the short tail moment, I decided to try again but being much more gentle. Set off at half throttle, resulting in fairly nice and gently climbing straight flight. However as soon as I tried to turn the plane settled back into its uncontrollable ways.

Eventually I nosed in and broke the motor mount, which was to be an easy fix. I then relaxed by flying my mini Infi, my dad getting some nice photos, before I landed it in a tree! Not the best of days

Only after getting home, re-setting the motor mount and contemplating the best way to lengthen the fuse to improve stability when I realised that the symptoms experienced (extreme instability, positive pitching moment) could be caused by a rearward CG.

Trying to find proof for this theory, I very carefully re-balanced the plane on a 25% CG point and found that the battery needed to be an inch further forward! Not quite sure how I managed that one, except enthusiasm over precision I guess

It rained all Sunday, so it looks like it’ll be a while before she flies again.

Hughbert
Nov 18, 2007, 10:08 PM
Come fly with me ...
It's still raining and with cold gusty winds! At least in Leeds!

Keep us all posted with your progress!
Nov 19, 2007, 06:15 AM
gpw
gpw
“There’s no place like Foam”
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Hugh , that looks Excellent !!! Where'd you get the strange spotted foam ... COOL stuff, eh???
Latest blog entry: Lost plans
Nov 19, 2007, 12:06 PM
Come fly with me ...
Your plane does look cool... where exactly did you get your foam (in the UK - B&Q?)

What foam is it exactly?
Nov 19, 2007, 01:52 PM
Planes are cool ;)
Hughbert's Avatar
Thread OP
Foam is EPP, ordered form www.eppfoam.co.uk. Its about £10 for 2 x 900mm x 600mm sheets for usual thickness (3mm, 5mm, 9mm, e.t.c.) and they sell in 3 colours - white, green and orange. I ordered white but they were out of stock so I accepted green instead, and I'm rather glad I did!

Just checked out the website and it says they're out of stock and to check back in a couple of days.

Unfortunately, although it didn't rain today it's dark when I get home from work so no flying maybe a few test glides in my back garden though...

Guess I'll work on the plan and decoration. Does anybody know how to add rulers to a JPEG, other than drawing one on myself, using usual or free software?

As for decoration, unsure to go for Aerobatic (cheques, flames, stripes, e.t.c.) or WW1 (roundels or maybe a lozenge...) since I'm pretty fond of both. May play with colour schemes and post some in a bit. Oh, and there will be a pilot...

Cheers for the kind words guys
Hugh
Nov 19, 2007, 05:40 PM
Use whatcha got!
msmith's Avatar
Keep us posted with the developments... Looks like a fun 'yard' flier... Might be something for some of my smaller gear for a full-house backyard aerobatic ship...

And I agree... that foam is too cool.

-mike
Nov 19, 2007, 08:11 PM
Come fly with me ...
Quote:
Originally Posted by Hughbert
Foam is EPP, ordered form www.eppfoam.co.uk. Its about £10 for 2 x 900mm x 600mm sheets for usual thickness (3mm, 5mm, 9mm, e.t.c.) and they sell in 3 colours - white, green and orange. I ordered white but they were out of stock so I accepted green instead, and I'm rather glad I did!
Might have to look at getting some of that, though I'm only just starting to get enough bits and pieces together to finish a balsa model (and two more balsa models coming soon - I hope!)

Quote:
Originally Posted by Hughbert
Guess I'll work on the plan and decoration. Does anybody know how to add rulers to a JPEG, other than drawing one on myself, using usual or free software?
Hugh
There's a few ways to do it. If you are hoping to get them printed, then you will need to know what size dpi you'll be printing at, then resize the rulers accordingly.

One of the easiest ways to add a ruler is to open a program that has rulers in there (MS Word, Adobe Photoshop, or something), press PrtScrn key (Print Screen) and then cut out the rulers in your favourite image editor and paste them onto the image, resizing as you go. Irfan view could probably do it, and it's free.

there'll also be some plugins for some of the image editors which would add a ruler. Hope this helps!
Nov 21, 2007, 04:42 PM
Planes are cool ;)
Hughbert's Avatar
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Ok, not much progress I'm afraid - still poor weather and darkness

I've messed with the plans and put a scale on (thanks chipko!) - not for measurements but to make sure they've printed to scale.

Also attached some prospective colour schemes; leaning more towards aerobatic than ww1 since I think it will come out looking too much like a 'tribute' SE5a, and I'd rather just build an SE and have this as something my own. Excuse the quality, they were all done in paint very quickly!

Anybody fancies 'colouring in' then you can use the jpeg in the first post - just remember the background colour has to be green!

Cheers all
Hugh

Edit - seems if you save the plan it resizes to something small. Am trying to get to grips with scaleandtile so will hopefully get something better going.
Nov 22, 2007, 06:37 AM
gpw
gpw
“There’s no place like Foam”
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Hug, what did it do on the maiden??? might benefit from a larger V Fin/Rudder???
Latest blog entry: Lost plans
Nov 22, 2007, 09:31 AM
Planes are cool ;)
Hughbert's Avatar
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Quote:
Hug, what did it do on the maiden??? might benefit from a larger V Fin/Rudder???
That's one of my thoughts at the moment; since that would improve stability.

On the first maiden it proved very 'squirrely' when any kind of control input was used. Although it would fly in a straight line at about half throttle, when I tried to turn it would go into a spiral, or over turn, or generally just tumble around. On full throttle it would pull upwards into a vertical climb, and when I tried to pull out it would do the tumble thing again.

I haven't been able to re-maiden it yet (is that a word?) and probably wont be able to till next weekend . At the field I just thought it needed bigger stabiliser surfaces but I realised when I got home it could be a CG thing, and when I then measured the CG at 25% chord, I had to make a drastic movement to the battery (1 inch) to get it to balance correctly.

My conclusion is obviously is that it needs more stability, and I have three changes planned; organised in difficulty of implementation. I will try the easiest first and if it doesnt work move onto the harder ones!

Change 1; move CG forwards
Change 2; increase stabiliser (v fin & h stab) area
Change 3; increase stabiliser moment e.g. make plane longer

I'm fairly sure that one or more of these will tame this beasty. All thoughts and advice are welcome!

Cheers
Hugh


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